The changes in sleep patterns that occur in human adolescence, when combined with other life issues at this age, may result in mood and behavioral disturbances. Adolescents with poor sleep patterns may also be at risk for poor school performance, excessive daytime sleepiness, increased drug and alcohol use, and increased risk of automobile accidents. A biological process may underlie the sleep pattern changes that occur at puberty, as the most prominent change appears to be a delay in the timing of sleep. The circadian system may undergo changes at puberty that lead to alterations in the timing of sleep. To investigate whether developmental changes occur in the circadian system peripubertally, an animal model system will be developed. A diurnal mammal, the Octodon degu, was chosen because the activity and sleep patterns approximate those of the human. In addition, although precocious at birth, a delay of four months precedes the onset of sexual maturation, which also models the situation in the human. Hypothesis 1, that sexual maturation is associated with a delay in phase of overt circadian rhythms, will be tested by examining phase of activity, wheel running and body temperature rhythms in entrained degus from 8 to 24 weeks of age. Hypothesis 2 is that circadian period (tau) lengthens in association with sexual maturation. This hypothesis will be tested in animals monitored in constant dim red light from 8 through 24 weeks. Specific aim 3 examines sleep patterns (EEG/EMG) of the Octodon degu across peripubertal range (ages 8-16 weeks) to examine the hypothesis that sleep phase delays in association with sexual maturation. The final specific aim of this small grant is to establish the time course of sexual maturation in the Octodon degu by measuring serum levels of sex steroids and luteinizing hormone across the putative phase of sexual maturation.